Effects of various co-solvents on the solubility between blends of soybean oil with either methanol or ethanol

To use the blends of low-carbon alcohols (methanol/ethanol) and soybean oil, a co-solvent seems to be necessary because of the unideal inter-solubility in the binary blends. There is only a few study works on the blending properties of soybean oil and ethanol with n-butanol as a co-solvent. In fact, more co-solvents should be investigated in order to use the blending fuel of soybean oil and low carbon alcohols. Therefore, in the current work, the co-solvents of butanol and its isomers together with polyoxymethylene dimethyl ethers (PODE) and tetrahydrofuran (THF) were used to investigate the effects of co-solvents on the inter-solubility between soybean oil and methanol/ethanol at ambient temperatures of 20 degrees C, 40 degrees C and 60 degrees C. Results show that all of tested co-solvents have the capacity to maintain stable one-phase in the binary systems of methanol/soybean-oil and ethanol/soybean- oil. For butanol isomers, n-butanol is a better co-solvent than that of 2-butanol and iso-butanol. PODE has better solubilization than that of butanol, while THF has the best solubilization in all test co-solvents. With the increase of ambient temperature, the additive amount of all kinds of co-solvents has a significant decrease, especially for the ethanol ternary system. The ternary system with ethanol has better inter-solubility than that of methanol system as using the same co-solvent. By adding methanol/ethanol and co-solvents into soybean oil, the viscosity of blending fuel is reduced and can match the conventional diesel fuel. Meantime, the higher density of PODE and THF has potential to improve engine performance. Finally, it can be concluded that both PODE and THF has better solubilization and fuel properties in the blends of methanol/ethanol and soybean oil.